Eurasion Blue Tit

Appearance

The Eurasian blue tit is usually 12 cm, long with a wingspan of 18 cm for both sexes, and weighs about 11 g.
A typical Eurasian blue tit has an azure-blue crown and dark blue line passing through the eye, and encircling the white cheeks to the chin, giving the bird a very distinctive appearance.

The forehead and a bar on the wing are white. The nape, wings and tail are blue and the back is yellowish green. The underparts is mostly sulphur-yellow with a dark line down the abdomen—the yellowness is indicative of the number of yellowy-green caterpillars eaten, due to high levels of carotene pigments in the diet. The bill is black, the legs bluish grey, and the irides dark brown. The sexes are similar, but under ultraviolet light, males have a brighter blue crown. Young blue tits are noticeably more yellow.

Naming

There are currently at least nine recognised subspecies:

⤷  "C. c. caeruleus" – : the nominate subspecies, occurring in Continental Europe to northern Spain, Sicily, northern Turkey and northern Urals
⤷  "C. c. obscurus" – : found in Ireland, Britain and Channel Islands
⤷  "C. c. ogliastrae" – : found in Portugal, southern Spain, Corsica and Sardinia
⤷  "C. c. balearicus" – : found on Majorca Island
⤷  "C. c. calamensis" – : found in southern Greece, Pelopónnisos, Cyclades, Crete and Rhodes
⤷  "C. c. orientalis" – Zarudny & Loudon, 1905: found in southern European Russia
⤷  "C. c. satunini" – Zarudny, 1908: found in the Crimean Peninsula, Caucasus, Transcaucasia and northwestern Iran to eastern Turkey
⤷  "C. c. raddei" – Zarudny, 1908: found in northern Iran
⤷  "C. c. persicus" – : found in the Zagros Mountains

Distribution

There are currently around 20–44 million pairs in Europe.

The Eurasian blue tit and the related hybrids are considered native species in areas of the European continent with a mainly temperate or Mediterranean climate, and in parts of the Middle East. These areas include Ireland, the United Kingdom and most of the European Union and EFTA, plus: Albania, Algeria, Andorra, Armenia, Azerbaijan, Belarus, Bosnia and Herzegovina, Georgia, Iran, Iraq, Jordan, Kazakhstan, Lebanon, Libya, the Republic of Macedonia, Moldova, Montenegro, Morocco, Russia, San Marino, Serbia, Syria, Tunisia, Turkey, Vatican City and Ukraine.

Status

The Eurasian blue tit is classified as a least concern species on the IUCN Red List, and as a Green Status species, since 1996, by the Royal Society for the Protection of Birds in the United Kingdom.

Behavior

Eurasian blue and great tits form mixed winter flocks, and the former are perhaps the better gymnasts in the slender twigs. A Eurasian blue tit will often ascend a trunk in short jerky hops, imitating a treecreeper. As a rule the bird roosts in ivy or evergreens, but in harsh winters will roost wherever there is a suitable small hole, be it in a tree or nesting box. They are very agile and can hang from almost anywhere.

This is a common and popular European garden bird, due to its perky acrobatic performances when feeding on nuts or suet. It swings beneath the holder, calling "tee, tee, tee" or a scolding "churr".Eurasian blue tits are able to culturally transmit learning to other tit species. An example of this, dating from the 1920s, is the ability to open milk bottles with foil tops, to get at the cream underneath.

Habitat

In Great Britain the Eurasian blue tit can be found in a variety of environments, and is typically found in deciduous woodland, parks, gardens and even in the centre of towns. Eurasian blue and great tits form mixed winter flocks, and the former are perhaps the better gymnasts in the slender twigs. A Eurasian blue tit will often ascend a trunk in short jerky hops, imitating a treecreeper. As a rule the bird roosts in ivy or evergreens, but in harsh winters will roost wherever there is a suitable small hole, be it in a tree or nesting box. They are very agile and can hang from almost anywhere.

Reproduction

The Eurasian blue tit will nest in any suitable hole in a tree, wall, or stump, or an artificial nest box, often competing with house sparrows or great tits for the site. Few birds more readily accept the shelter of a nesting box; the same hole is returned to year after year, and when one pair dies another takes possession. It is estimated by the RSPB that there are 3,535,000 breeding pairs in the UK.

During the incubation period, female blue tits perform all of the incubation, however the male feeds the female during this time. During the nestling period both female nest attendance and male feeding rate are higher in the morning, declining throughout the day.

Eggs are 14–18 mm long and 10.7–13.5 mm wide. Egg size appears to depend mostly on the size of individual females and secondarily on habitat, with smaller eggs found at higher altitudes. The clutch's total weight can be 1.5 times as heavy as the female bird.

A study found that the timing of breeding in blue tits is related to the expression of nestling carotenoid‐based coloration, which could play a role in offspring–parent communication.

The bird is a close sitter, hissing and biting at an intruding finger. In the South West of England such behaviour has earned the Eurasian blue tit the colloquial nickname "Little Billy Biter" or "Billy Biter", originating from the UK. When protecting its eggs it raises its crest, but this is a sign of excitement rather than anger, for it is also elevated during nuptial display. The nesting material is usually moss, wool, hair and feathers, and the eggs are laid in April or May. The number in the clutch is often very large, but seven or eight are normal, clutch size varies with latitude and other geographic parameters. Some bigger clutches may be laid by two or even more hens in some locations but single hen clutches of 14 have been verified in the UK. It is not unusual for a single bird to feed the chicks in the nest at a rate of one feed every 90 seconds during the height of the breeding season. In winter they form flocks with other tit species.

Food

The Eurasian blue tit is a valuable destroyer of pests, though it is fond of young buds of various trees, especially when insect prey is scarce, and may pull them to bits in the hope of finding insects. It is a well-known predator of many Lepidoptera species including the Wood Tiger moth. No species, however, destroys more coccids and aphids, the worst foes of many plants. It takes leaf miner grubs and green tortrix moths. Seeds are eaten, as with all this family, and blue tits in British urban areas have evolved the ability to digest milk and cream.

Predators

The small size of the Eurasian blue tit makes it vulnerable to prey by larger birds such as jays who catch the vulnerable fledglings when leaving the nest. The most important predator is probably the sparrowhawk, closely followed by the domestic cat. Nests may be robbed by mammals such as weasels and red squirrels, as well as introduced grey squirrels in the UK.

The successful breeding of chicks is dependent on sufficient supply of green caterpillars as well as satisfactory weather. Breeding seasons may be affected badly if the weather is cold and wet between May and July, particularly if this coincides with the emergence of the caterpillars on which the nestlings are fed.

Cultural

The Eurasian blue tit has appeared on many stamps and ornaments. Its most recent appearance on a British stamp was the 2010 "Birds of Britain" series.